code: def register_ray_trainer(model_type: str, default=False):
      """Register a trainer class that supports training the given model types with Ray backend.
  
      Using default=True will make the trainer the default trainer for the model type.
  
      Args:
          model_type: The model_type which dictates the trainer type to use.
          default: Whether the trainer should be the default trainer for the model type.
      """
  
      def wrap(cls):
          _ray_trainers_registry[model_type] = cls
          if default:
              if DEFAULT_KEYS[0] in _ray_trainers_registry:
                  raise ValueError(
                      f"Default trainer already registered for model type {model_type}"
                  )
              for key in DEFAULT_KEYS:
                  _ray_trainers_registry[key] = cls
          return cls
  
      return wrap
  
file_path: ludwig/ludwig/trainers/registry.py
imports: from ludwig.api_annotations import DeveloperAPI
  from ludwig.utils.registry import DEFAULT_KEYS, Registry
label_desc: Use image node_id 6 for calling a global function with example usage: register_ray_trainer(model_type, default) and returns: wrap, cls